1. Field of the Invention
Embodiments of the present invention generally relate to a system and process for screen printing a multiple layer pattern on a surface of a substrate.
2. Description of the Related Art
Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical power. Solar cells typically have one or more p-n junctions. Each p-n junction comprises two different regions within a semiconductor material where one side is denoted as the p-type region and the other as the n-type region. When the p-n junction of a solar cell is exposed to sunlight (consisting of energy from photons), the sunlight is directly converted to electricity through the PV effect. Solar cells generate a specific amount of electric power and are tiled into modules sized to deliver the desired amount of system power. Solar modules are joined into panels with specific frames and connectors. Solar cells are commonly formed on silicon substrates, which may be single or multicrystalline silicon substrates. A typical solar cell includes a silicon wafer, substrate, or sheet typically less than about 0.3 mm thick with a thin layer of n-type silicon on top of a p-type region formed on the substrate.
The PV market has experienced growth at annual rates exceeding 30% for the last ten years. Some articles suggest that solar cell power production world-wide may exceed 10 GWp in the near future. It is estimated that more than 95% of all solar modules are silicon wafer based. The high market growth rate in combination with the need to substantially reduce solar electricity costs has resulted in a number of serious challenges for inexpensively forming high quality solar cells. Therefore, one major component in making commercially viable solar cells lies in reducing the manufacturing costs required to form the solar cells by improving the device yield and increasing the substrate throughput.
Screen printing has long been used in printing designs on objects, such as cloth or ceramics, and is used in the electronics industry for printing electrical component designs, such as electrical contacts or interconnects on the surface of a substrate. State of the art solar cell fabrication processes also use screen printing processes. The mis-alignment of a screen printing pattern on a substrate surface due to errors in the positioning of a substrate on the automated transferring devices, or defects on the edge of the substrate, can lead to poor device performance, and thus device yield issues. Manual calibration of the positioning of the substrate within the system can be time consuming and require frequent adjustment based on differences in batches of substrates or drift in the calibrated position of the substrate.
Therefore, there is a need for a screen printing apparatus for the production of solar cells, electronic circuits, or other useful devices that has an improved method of controlling the device positioning within the system, increased throughput and a lower cost of ownership than other known apparatuses.